PROJECT SUMMARY How information is transformed as it propagates through a neural circuit remains an outstanding question of modern neuroscience. Answering this question for a given circuit requires knowledge of: 1) the information being transformed, 2) activity in pre- and postsynaptic populations, and 3) connectivity between pre- and postsynaptic populations. The tremendous complexity of neural circuits has made such investigation exceedingly difficult, with success limited to small local circuits or across gross brain regions. The overall goal of this project is to bridge these scales to map the transformation of information across a large neural circuit through technological advances in large-scale monitoring of neural activity and quantitative analyses of high-dimensional neural representations. A secondary goal of this project is to develop a platform for monitoring the transformation of information in a well-defined circuit amenable to the application of interventional tools capable of causally linking circuit elements to aspects of neural coding. To accomplish these goals, this project will capitalize on recent advances in spectrally separated calcium indicators of neural activity and the unique circuitry of the mammalian olfactory system to simultaneously image sensory-evoked activity in large pre- and postsynaptic neural populations while selectively manipulating specific interneuron classes. The resulting dataset will enable multiple exploratory analyses of high-dimensional neural representations as well as hypothesis-driven analyses of how the olfactory system transforms information, including investigating the organization and neural coding roles of interneuronal networks. This project will thus provide fundamental new insight into brain function by exploring how information is transformed across a large neural circuit, and will further generate key advances in the fields of systems neuroscience and olfaction.